Arc welding of unalloyed structural
steel workpieces such as hull-plates,
and arc welding electrodes therefor



United States Patent US. Cl. 219-137 3 Claims Matter enclosed in heavybrackets II] appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

This invention relates to electric arc welding and especially to thewelding of ship hulls or other steel structures subjected to immersionin sea water.

Among the various type of electrodes which may be employed for thewelding of the joints between ship hull plates, the lime-fluoride coatedelectrodes have gained a wide popularity on account of their suitabilityfor octof-horizontal welding as well as on account of the excellentmechanical propertes of the welds produced. Cases have been reported,however, in which hull plate welds produced with basic-coated electrodeshave been subjected to severe corrosion of a kind not observed in weldsmade with other electrode types. Investigations have disclosed the factsthat the joints attacked by this kind of corrosion were always situatedbelow the waterline, and that the protective paint had been destroyed orremoved not only from the welds but also from the adjoining plates.Particularly bad cases of corrosion have occurred in ice-breakers. Theswift progress of the corrosion in said cases is explained by the factthat the protective paint is scraped away and the welds continually keptclean of corrosion products by the action of the ice.

It is an object of the invention to provide an improved structural steelWelding process in which lime-fluoride coated electrodes are used butthe resulting welds are substantially proof against abnormal corrosionin sea water. It is also an object of the invention to provide improvedwelding electrodes of the lime-fiuoride type adapted to provide asubstantially unalloyed steel weld deposit not liable to preferentialattack in sea water. Another object is the provision of lime-fluoridecoated welding electrodes which, while having the new property justindicated, still retain their general usefulness and may be generallyemployed in the same fields as ordinary unalloyed steel lime-fluorideelectrodes.

Other objects and features of the invention will be apparent from thefollowing specification and the claims.

The improved process according to the invention is applicable to thewelding of joints between unalloyed structural steel workpiecessubjected in use to immersion in sea water. The steels here designatedas unalloyed structural steels should be understood to comprise not onlyplain low carbon steels, but also steels containing moderate proportionsof silicon and manganese, for instance up to 0.7% silicon and up to 1.5%manganese, added as deoxidizing agents or for the purpose of adjustingthe tensile strength of the steel. In most cases, the contents ofcarbon, silicon and manganese in ship hull steels do not exceed thefollowing percentages: C 0.25%, Si 0.30%, Mn 0.90%. According to a basicfeature of the process according to the invention, the joints are weldedwith lime-fluoride coated electrodes so composed as to produce a lowcarbon unalloyed steel weld deposit containing additions of at least onemetal soluble in ferrite and having a lower (less negative)electrolytical potential than iron, the addition of said metal being soadjusted that the electrolytical potential of the weld deposit in seawater is approximately equal to or slightly less negative than thepotential of the workpiece material.

In this connection, lime-fluoride coated electrodes should be understoodto comprise any coated electrodes in which the slag-forming constituentsof the coating substantially consist of limestone (which may be whollyor partly replaced by other alkaline earth carbonates, for instancedolomite) and fiuorspar (which may be wholly or partly replaced bycryolite or similar double fluorides). The expression low carbonunalloyed steels should be understood to mean steels which contain notmore than 0.25% of carbon, preferably not more than 0.1%, and which maycontain, in addition to the special metals to be added according to theinvention, silicon and manganese in the proportions usually employed insteel weld deposits for deoxidizing purposes or for adjusting thetensile strength of the steel, for instance 0.7% silicon and 1.5%manganese. The weld deposit may also contain small proportions of otherelements sometimes employed in unalloyed steel weld deposits, forinstance titanium and aluminum, as well as usual impurities among whichchromium in amounts up to 0.1% is to be counted. The total content ofmetals other than iron, copper and nickel should not exceed 2.5% byweight.

The preferential corrosion of the welds to which reference has been madeabove can be explained as an effect of the formation of galvanicelements in which the weld is the negative electrode and the parentmaterial (the plate) is the positive electrode. This kind of corrosionwill be completely suppressed in welds produced according to theinvention. Owing to the fact that different classes of structuralplates, and even diflerent consignments of plates of one class, willrarely have the same potential, it will be difficult to carry out theprocess according to the invention in such a manner as to make thepotential of the weld deposit exactly similar to the one of thesurrounding plates. However, no such exact adjustment of the welddeposit potential will be required, as the intended object will berealized just as well by displacing the weld deposit potential in thepositive direction by an amount sufficient to make the weld depositconstitute the positive electrode of the galvanic elements formed withall of the plate materials employed. Under these conditions, thegalvanic current produced cannot result in any dangerous corrosion, asthe current density at the surface of the plates constituting thenegative electrode will be too small to produce any corrosive effects.As a practical rule ,the composition of the weld deposit should beadjusted so as to result in a potential (in sea water) in theapproximate range between the potential of the workpiece material and anupper limit about 5 millivolts less negative than the potential of theworkpiece material.

The preferred metals to be added in the process according to theinvention are copper and nickel, singly or in combination. While cobaltmay be considered an equivalent to nickel, the former metal has noparticular advantages to justify its higher price. To produce asubstantial reduction of the tendency to corrosive attack on the weld,the proportion of copper plus twice the proportion of nickel present inthe weld should amount to not less than 0.5% by weight. Therefore, ifcopper alone is added, the proportion of copper should be at least 0.4%

3 by weight, while, if nickel alone is added, a proportion of 0.2% byweight will be sufiicient.

The welding electrode according to the invention comprises a core of lowcarbon unalloyed steel and a coating of the lime-fluoride type havingsuch a composition that the electrode will produce a weld deposit of lowcatbon unalloyed steel. According to the invention, the electrodecontains such a proportion of copper and/or nickel that the sum of thecopper content and twice the nickel content constitutes at least about0.4%, preferably not less than 0.6% by weight of the metallicconstituents of the electrode. The total content of said metals shouldnot exceed 1.25% by weight of the metallic constituents of theelectrode. The metal or metals added may be present as constituents ofthe metallic core or as constituents of the coating, or as constituentsof both. If copper is employed, the core wire may for instance contain0.2% of copper, while the remainder of the proportion of copper requiredis added as a constituent of the coating. The copper may be present inthe coating in the form of a copper oxide. The welding process willreduce the copper oxide to metallic copper. If copper alone is employed(no nickel or cobalt), a proportion of copper amounting to about 1% byweight of the metallic constituents of the electrode can be recommendedas suitable for the majority of practical cases.

While it has not yet been possible to obtain complete clarity concerningthe metallurgical factors determining the intensity of the preferentialattack on the weld deposit produced with ordinary limefiuoride coatedelectrodes, it is believed that the comparatively large proportion ofsilicon usually present does play an important part. The inventiontherefore is of particular interest in connection with the usual kind oflime-fluoride coated electrodes in which the coating contains a weightof silicon, usually in the form of ferrosilicon, amounting to not lessthan 0.5% by weight of the metallic constituents of the electrode.

An example of a welding electrode according to the invention will now begiven. The core wire has a diameter of 4 mm. (0.158 in.) and consists ofmild carbon steel (C 0.010%). The extruded coating has an outer diameterof 6.3 mm. (0.248 in.) and is composed as follows (exclusive of thepotassium silicate binder) The weld metal deposited with this electrodehas a copper content of approximately 0.7%. An all Weld metal test barhad a potential of 736 millivolts in sea water at 25 C. against astandard electrode. Test bars made from normal ship plate had under thesame conditions potential between 735 and --738 millivolts. All weldmetal test bars made with normal, practically copper-free lime-fluoridecoated electrodes will assume potentials between 742 and 747 millivolts.

Corrosion tests have been carried out in which welded plate samples weresubmerged in the sea for extended periods and the corrosion products asWell as other contaminations Were removed at regular intervals. Thewelds produced with ordinary, practically copper-free lime-fluoridecoated electrodes were preferentially attacked resulting in theformation of a groove the bottom of which was formed by the weld surfaceand the depth of which increased throughout the immersion period. Incontradistinction thereto, the welds made with the welding electrodesaccording to the present invention exhibited normal rusting only andwere not attacked more intensely than the adjoining plate material.

We claim:

1. An arc welding electrode comprising a core of lowcarbon unalloyedsteel and a coating of the lime-fluoride type, characterized by acontent of metal from the group comprising copper, nickel, and cobalt,the total weight of metal from said group not exceeding 1.25% of theweight of all of the metallic constituents of the electrode, and theweight of copper plus twice the combined weight of nickel and cobaltamounting to not less than 0.4% by weight of all of the metallicconstituents of the electrode.

2. An arc welding electrode comprising a core of low carbon unalloyedsteel and a coating of the lime-fluoride type, said coating comprising aweight of silicon, preferably in the form of ferrosilicon, amounting tonot less than 0.5% of the weight of all of the metallic constituents ofthe electrode, characterized by a content of copper amounting to notless than 0.6% and not more than 1.25 of the weight of all of themetallic constituents of the electrode.

3. In the arc welding of joints between unalloyed structural steelworkpieces and subjected in use to immersion in sea water, the step ofwelding said joints with limefiuoride coated electrodes producing a lowcarbon unalloyed steel weld deposit containing additions of at least onemetal from the group comprising copper, nickel, and cobalt, the totalweight of metal from said group not exceeding 1.25% of the weigth of allof the metallic constituents of the eletcrode, and the weight of copperplus twice the combined weight of nickel and cobalt amounting to notless than 0.4% by weight of all of the metallic constituents of theeletcrode, the addition of metal from said group giving the electrolyticpotential of the weld deposit in sea water a value substantially in therange between the potential of the workpiece material and an upper limtabout 5 millivolts less negative than the potential of the workpiecematerial.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,704,317 3/1955 Hummitzsch et al. 219146 FOREIGNPATENTS 420,277 11/ 1934 Great Britain. 553,371 5/1943 Great Britain.

ANTHONY BARTTS, Primary Examiner C. L. ALBRITTON, Assistant ExaminerU.S. Cl. X.R. 219-146

3. IN THE ARC WELDING OF JOINTS BETWEEN UNALLOYED STRUCTURAL STEELWORKPIECES AND SUBJECTED IN USE TO IMMERSION IN SEA WATER, THE STEP OFWELDING SAID JOINTS WITH LIMEFLUORIDE COATED ELECTRODES PRODUCING A OWCARBON UNALLOYED STEEL WELD DEPOSIT CONTAINING ADDITIONS OF LEAST ONEMETAL FROM THE GROUP COMPRISING COPPER, NICKEL, AND COBALT, THE TOTALWEIGHT OF METAL FROM SAID GROUP NOT EXCEEDING 1.25% OF THE WEIGTH OF ALLOF THE METALLIC CONSTIUENTS OF THE ELETCRODE, AND THE WEIGHT OF COPPERPLUS TWICE THE COMBINED WEIGHT OF NICKEL AND COBALT AMOUNTING TO NOTLESS THAN 0.4% BY WEIGHT OF ALL OF THE METALLIC CONSTITUENTS OF THEELETCRODE, THE ADDITION OF METAL FROM SAID GROUP GIVING THE ELECTROLYTICPOTENTIAL OF THE WELD DEPOSIT IN SEA WATER A VALUE SUBSTANTIALLY IN THERANGE BETWEEN THE POTENTIAL OF THE WORKPIECE MATERIAL AND AN UPPER LIMITABOUT 5 MILLIVOLTS LESS NEGATIVE THAN THE POTENTIAL OF THE WORKPIECEMATERIAL.